Electronic implants have been used in modern medical technology as microstimulators having diverse embodiments, and are used, for example, as cardiac pacemakers, defibrillators (ICDs, CRT-Ds, etc.) and/or neurostimulators.
Such implants generally have a number of electrical contacts which are used to receive and transmit electrical pulses measured by probes, and electrode leads are provided that transmit stimulating signals from a control unit to one or more implanted electrodes for stimulation. For example, a cardiac pacemaker can detect the excitation pulses of the heartbeat generated by the sinoatrial node and output stimulating electrical signals to one or more stimulating electrodes on the heart if aberrations are present, e.g., in the pulse rate.
Such an implantable arrangement for stimulation is described in U.S. Publication No. 2008/0154320, for example. The cardiac pacemaker described in that publication is comprised of a housing, in which a battery and the biometric evaluation and control electronics and, in particular, a capacitor are accommodated, the capacitor being used to generate and transmit electrical stimulating pulses to at least one electrode lead extending out of the housing.
The requirements on the quality of the transmitted signals is very high, of course, in particular for excitation pulses that act directly on central functions of human organs. This applies for the precise, time-based output of an excitation pulse or a sequence of pulses, and for the regulation and stabilization of the suitable pulse shape and electrical intensity.
The properties of the capacitor integrated in the implant determine, to a non-insubstantial extent, the intensity and quality of the transmitted signal shape that can be achieved. U.S. Publication No. 2008/0154320 therefore proposes the use of special oxides to form a separating layer between the anode and the cathode of the capacitor, which has high dielectric constants and, therefore, provides the greatest possible capacitance combined with the smallest possible capacitor volume.
Implanted stimulators can now remain in the human body for years in some cases. A requirement therefore is that the housing and the electrode leads of such an implant be comprised of a material that has the highest possible biocompatibility, thereby ensuring that no substances are released into the body that could cause metabolic harm.
Every implant that is installed in the human or other body is surrounded for the entire operating period by a physical medium, namely, a mixture of various chemical components that is relatively reactive due to the different dissolved ions in particular. A permanent hermetic seal of the implant housing must therefore fulfill special requirements. The purpose thereof is to prevent bodily fluid from entering the implant and thereby ensure that all internal electronic components are protected, and to prevent substances (battery media, capacitor electrolytes, etc.) that are present in the interior of the implant and could harm the organism from escaping and entering the physical medium.
The seal in the region of a feedthrough hole of an electrode through an opening in the housing wall of the implant is particular problematic in that particular case. To ensure that the external physical medium and, e.g., electrolyte present inside the capacitor are reliably separated in this region, the seal must be comprised of a non-ageing material which has appropriate mechanical properties for a seal and is stable against the chemical effects of bodily fluid and the substances that may be adjacent thereto on the internal side.
High requirements are also placed on the feedthrough holes in the electronic components used in the implant, in particular, in batteries and/or capacitors. For example, the electrical feedthrough holes in a capacitor must function as a barrier to the electrolytes that cannot be overcome, at least for the duration of the expected service life of the implant, in order to protect the interior of the implant against leaking electrolyte solution, and to safeguard the functionality of the capacitor and, therefore, the implant.
To this end, the metallic electrode in the feedthrough hole is typically enclosed by elastic sealing material in the region of the passage. Elastomer-based plastics are suitable, for instance, and, in the case of an electrically conductive housing material, the sealing material simultaneously functions as electrical insulation. In the process of fabricating a permanent hermetic seal of the electrode feedthrough hole, all surface patches that abut one another, i.e., between the electrode and the sealing material, and between the sealing material and the housing wall, must therefore be joined to one another in a manner free of joints and pores.
U.S. Pat. No. 7,365,960 relates to this technical field. It describes an electrode feedthrough hole of a capacitor for implants that is sealed using a specially formed sealing flange.
FIGS. 1A and 1B (prior art) show a cross section of the electrode feedthrough hole and the sealing flange inserted therein, according to U.S. Pat. No. 7,365,960. FIGS. 1A and 1B are reproductions of FIGS. 11 and 12 of the '960 patent and, accordingly, the same reference numbers as used in the '960 patent are provided thereon. However, only a general description of these figures will be provided herein. In general, the sealing flange, which is comprised of rubber or elastic plastic, has an inner feedthrough hole through which a conductive connecting piece of the capacitor disposed in the implant extends. The connecting piece is designed as a hollow cylinder into which the further-extending electrode lead is inserted centrally from the outside. Since the feedthrough hole of the sealing flange has a cross section that is smaller than the electrode diameter (see FIG. 1B), pressure is generated when the arrangement is assembled, thereby ensuring that a seal exists between the electrode and the flange. To form the seal against the housing, the flange comprises an outer, annularly circumferential groove, into which the housing wall engages after the flange has been inserted. The dimensions of the groove are also intended to be slightly smaller than the thickness of the housing wall, and therefore the elastic sealing material rests tightly against the housing wall on both sides after the flange has been inserted into the housing opening.
The arrangement provided for the feedthrough of a capacitor contact for implants has the disadvantage that production is relatively costly due to the special shaping of the sealing flange since the circumferential groove of the flange must fit precisely into the housing opening when the arrangement is assembled. In addition, the electrical feedthrough using a plug connection between the further-extending, outer electrode lead and the metallic connecting piece to the capacitor requires that these transition pieces be produced with the most exact fit possible and be joined accordingly.
The present disclosure is directed to a feedthrough conductor for implants as, for example, disclosed in U.S. Pat. No. 7,365,960, as the closest prior art. The problem to be solved is that of developing a feedthrough conductor for electronic components, such as those used in permanently implantable stimulators, which meets the requirements for sealing and has additional advantages, thereby ensuring that the electrode, sealing material, and housing may be easily joined. A further problem to be solved by the disclosure is that of providing such a feedthrough conductor for capacitors, in the case of which the electrode surface of the capacitor contact can also be shaped and anodized up to a defined region of the feedthrough hole.
The present inventive disclosure is further directed toward overcoming one or more of the above-identified problems.